Tie trunk line



y 21, 9 1.. J. BOWNE 2,002,218

T'IE TRUNK LINE Filed Aug. 22, 1954 T/Nl/EN TOR y L. J. BOWNE ATTORNEY Patented May 21, 1935 I Y UNITED STATES PATENT OFFICE V TIE TRUNK LINE Langford Bowne, Howard Beach, N. Y., as- .signor, to Bell Telephone Laboratoriealncorporated, New York, N, Y., a corporation of New York l Application August 22,1934; Serial No. 740,889

Claims. (01. 179-43) This invention relates to telephone systems and and circuits are associated with the tie line at the more particularly to what are known as tie trunk Switchboard X as indicated y the broken line lines for interconnecting private branch exchange box LCX. i

switchboards. I Relay 1 in operating closes a locking circuit 5 The objector the invention is to simplify and for ts lf fr m und at its lower nta 6 improve the efiiciency of such trunk lines and t ugh ts l e Winding t0 batteryfit the pp particularly the means'for signaling and supercontacts of relay 8. Operation of relay 1 e150 vision thereover. closes a circuit to light the line lamp 9 which A feature of the invention resides in means as' c e tweed from ground, Contact of relay sociated'with each end of the "trunk line for dista ts ll f r y 8 and mp 9 t tt y. 10

criminating between ringing current incoming Th p r r t he privat branch exchange a over the line' from the distant switchboard and Y upon noting t h d l mp 9 s ts plu 3 ringing current applied at the near switchboard 0f 60rdeilellit CY iIltO jack 2 thereby Closing whereby incoming ringing current is prevented the auxiliary ta lief the a k t p at from directly affecting the apparatus of a conrelay 5 which, in pe t Opens its uppermost 16 nected common battery cord circuit by opening Contacts thereby breaking the leekihg Circuit for one of the trunk line conductors anda direct currelay 7 and Opening the Circuit a p 9 t rent bridge across theline is opened to control contacts ithe cord supervisory signal in the usual manner Relay in pe e150 Connects ground, at

and whereby outgoing ringing current remov its contacts 13, to the sleeve of the jack 2, and 20 the direct current bridge and closes the line to all ether jack sleeves'which m b mu tipled conductor to enable the ringing current to be h whereupon the c up v ry amp 3 transmitted over the trunk line to the distant end. is lighted in the usual manner- When ay 8 other fe t re t specifically mentioned W111 operated it also closed at its contacts 14 a circuit "be apparent from the following description when threush resistance 1 to p t ay 6. 25

read in conjunction with the accompany draw- The operation of relay l8 opens, at its contact ing which shows a two-way manual ring dow 't H, the normally closed shunt, including the reline in accordance withthe invention which ter- Sistanee around the p Condenser 6 85, minat at h end i pr t branch exchange at its lower contacts, the ring side of the line i Switchboard and at its contact 20 connects a bridge, compris- 30 For purposes of description, it will be assumed ns inductance 2| d a p e es sta ce 2, that subscribers stations A and B are connected across e line conductors to p ate the cord to and served by private branch exchange switoh- Supervisory relay 24 in t a we in cord, which boards X and Y respectively and that extending relay open its t t and t iS eS the subetweeri these switchboards' is a two-wayring pervisely'iemp Opelatien f e ay 6 also 5 w t trunk line in accordance t 't prescloses its contact 25 which connects condenser ent invention which terminates at switchboard X 25, on m e with Condenser the P p Of in jack I and atswitchboard Yin jack 2. w 'later appear,

. L t it b further a d that Subscriber A The extension of the call to subscriber B will "40 siring to communicate with subscriberBhas called be effected by the other end of 9 CY in the 40 and then answered by the operator at switchusual mannerboard X by inserting plug 3 of the cord circuit When the conversation between the connected into the calli bs ibe 1mg jack 4, Upon stations is terminated the operators at each ascertaining that subscriber B is desired, which Switchboard are pp d- Of t s fact in the station is r ach d i th h t k line T-and usual manner and break the connection by reswitchboard Y, the operator at switchboard X moving the respective 9 i 'p s rom the ins rt th lli plug 5 of t cord t, t subscribers line and tie line whereupon the tie the line jack I of the tie line and applies ringing line circuit is restored to nermel- In case, wcurrent to the line by operating the ringing key 6 ever, the p a at w t a d X, f r exthereby causing the obvious operation of the rih ample, should desire to recall the operator at 50 up relay 1 at the distant end of the tie line. switchboard Y before that operator has removed At this point it may be mentioned that the tie the plug 34 from jack 2, she may do so in the line circuit apparatus withinthe broken line'box usual manner by ringing on the line whereupon LCY is located at the switchboardgor private relay 7 operatesas before but does not lock up branch exchange Y, and that identicalapparatus due to the fact that its locking circuit is open switchboard cnd of the line, similar apparatus- ,and circuits at the other or X switchboard end erating the cord supervisory relay 24 which wasreleased when the bridge 2 I, 22 was opened thus lighting the cord supervisory lamp 23 as a recall signal.

As before mentioned, the tie-line T is a-twoway circuit, that is to say, it is arranged to opcrate in either direction and consequently each end is equipped with thesame, apparatusand circuit connections although for the sake of brevity apparatus has only been shown at the Y being indicated by the dotted line box LCX.

,Due to the fact/that certain other relay operations take place atthe end of the line at which 7 a call is initiated an outgoing or originating call from the private branch exchange Y will now be described.

Toinitiate an outgoing call from the switchboard Y the operator may insert either end of the cordcircuit CY in the jack 2. 7 If we assume thatplugsd is; used the operator plugs in and rings byoperating the ringing key 29 which lights ,line lamp 30 attheswitchboard X in the manner previously described forlighting the lamp 9 on a call in the opposite direction.

When theoperator plugs in the auxiliary jack contacts iii are closed thereby operating relay 8 which in, turn operatesrelay l6. Relay l6, as before described, opens its contact I! thereby re- -.moving the shunt around condenser 19, opens the ring side of theline, connects the bridge 2|, 22 across the tip and ring of the line at its contacts j 20 and at contacts 25 connects condenser 26 in parallel with condenser which latter con-' denser is; in series with ringing relay 3! across r the line.

When the operator actuatesringing key 29 alternating current is applied to the tip and ring of; the line which causes relay 3! to operate. It

7 may bementioned at this time that condenser E! is of too low capacity by itself to pass sufficient current to operate relay 3| in multiple with the ;.i nductan oe and resistance bridge 2|, 22 but the combined capacity of condensers 2E and 27 in parallel enables relay 3| to attract its armatures. When relay 3| closes itsupper contacts it short circuits relay I6 which circuit can be traced from H ground, upper contacts of relay 3|, contacts 28 the ,c,ondenser ;26 from condenser 21.

of-relay 8, now operated, toone terminal of the winding of relay is, the other terminal of which .is. permanently grounded. This causes relay it to release which reclosesat its contacts I1, the shunt circuit around condenser l9 thereby pass .ing insuflicient ringing current over the line to ...operate the ringing relay at the distant end.

Release of relay ls also opens its contacts 20 and 25 which open the bridge 2!, 22 and disconnect Sufficient currentis now passedby COn enser 2'! alone due tothe disconnection of the bridge 2|, 22 to hold relay ,3ioperated during; the ringing interval. Closure, of the lower contacts of relay 3| shunts.

- ,.the ringcondenser 32 and the now open lower 1contactstoirelay;l6,;;by resistance 33, thereby as 3 is removed from the line jack, to such a value as not to operate the ringing relays, such as i, connected across the two ends of the line.

What is claimed is:

1. In a telephone system, a twoway trunk line, an operators position terminating one end thereof, a link circuit and an associated source of alternating ringing current at said position and adapted to be connected to said trunk line, means for connecting said source to said trunk line by way of said link circuit, a direct current bridge circuit at said position adapted to be connected across the trunk line, an alternating current bridge circuit including a first condenser connected across the line at said position, a second condenser adapted to be connected in multiple with said first condenser, means responsive to the connection of said link circuit to said trunk line to connect said direct current bridge circuit across said trunk line and connect said second condenser in multiple with the first condenser, and a relay in said alternating bridge circuit responsive to connection of said current source to said trunk line by way cfsaid link circuit to disconnect said direct current bridge and said second condenser during the interval said current source is connected. 7

2. In a two-way ring-down trunk line having one conductor normally open at one end, means responsive to the establishment of a connection with the line at said one end for closing said open conductor, introducing a condenser in the other line conductor and connecting a direct current bridge across the line on the switchboard side of said condenser and said point of closure, and discriminating means responsive to the application of ringing current at the distant end of the line for reopening said line conductor, shunting said condenser and removing said bridge and responsive to application of ringing current at the near end of the line for shunting said condenser and removing said bridge only.

3.111 a telephone system, near and distant switching stations, a relay at each station; line conductors extending between said stations one of said conductors being normally opened at contacts of each relay, a condenser in each end of the other line conductor, a direct current shunt aroundeach condenser including normally closed contact oi'its respective stationrelay, a link circuit at each station adapted to be connected to said line conductors, a source of alternating ringing current associated with each link and means for connecting said sources to their respective ends of the line, a direct current bridge including inductive and non-inductive resistances adapted to be connected across the line at the near end by the station relay thereat, an alternating current bridge of relatively low capacity connected across the near endof the line, a circuit of predetermined capacity, adapted to be connected in multiple with a portion of said alternating current, bridge by the respectivestation relay to increase the capacity of said bridge, means responsiveto the connection. of the'link circuit with the near end of the line to operate the station relay thereat, thereby closing the normally opened line conductor there-at, opening the respective line condenser shunt, connecting the direct current bridge across the line and increasing the capacity of the alternating current bridge by connecting said multiple circuit therewith, said alternating current bridge including a relay thereafter responsive to the connection of said ringing source to the near end of the line to release said first relay and shunt the contacts thereof normally opening said line conductor when said relay is released. v

4. In a telephone system, a two-way ring-down trunk line adapted to be connected to a common battery cord circuit at one end, signal apparatus connected to said line at each end thereof, a direct current bridge circuit adapted to be connected across said one end of the line responsive to connection of said cord circuit with said line thereat said bridge circuit serially including an inductance, and a pure resistance, said inductance and saidresistance having such values and so proportioned with respect to each other as to possess a high impedance to speech frequency, to

have a sufliciently low direct current resistance to operate the cord supervisory relay connected to the line and to limit the inductive surge through said inductance when said cord circuit is disconnected from the line to a value inefiective to falsely operate the signal apparatus connected to the line.

5. In a telephone system, a trunk line, a cord circuit adapted to be connected to one end of said line, a source of alternating ringing current associated with said cord circuit and adapted to be connected therein to said line, an alternating current bridge circuit serially including a condenser and a relay connected across said line at said one end, a second condenser adapted to be connected in multiple with said first condenser to increase the capacity of said bridge and means operated in response to connection of said circuit with said line to connect said second condenser in multiple with the first condenser, said relay in series with the multiple capacity being responsive to connection of said source to the line to release said means and thereby reducing the capacity of the bridge.

LANGFORD J. BOWNE. 

